Ag-doped SnO2 thin films are deposited on Al2O3 substrates by spin-coating using unalcolate sol-gel synthesis.The analysis from AFM and FE-SEM micrographs indicates the crystal grains are spheric

and the size of grains is about 20 nm with 600 ℃ sintering temperature and increases with calcing temperature increasing.Gas sensitivity is tested by a static state method.The sensitivity of Ag-doped SnO2 thin films is 32.7 for volum fraction of 50×10-6 alcohol vapor and is 4.9 for the same concentration gasoline vapor.The results show that Ag-doped SnO2 increases alcohol sensitivity and reduces gasoline sensitivity and improves selectivity.Under direct-current heating voltage the sample’s resistance and capacitance have more change early day and go to stabilize with aging time prolonged.Complex impedance analysis shows that long-term stability is relational to the change of resistance and capacitance at the grain boundary which consists in the change of height and breadth of grain boundary barrier.The change essence possible comes from the ionic transfer among grain boundary layer under direct-current biased voltage